M2M Communication (Machine Type Communication; MTC)
Hereinafter, machine-to-machine (M2M) communication (or machine type communication (MTC)) will be described in brief.
Machine-to-machine (M2M) communication may denote communication between an electronic device and an electronic device as its expression. In other words, M2M communication may denote communication between objects. In general, M2M communication may denote wired or wireless communication between electronic devices or communication between a human-controlled device and a machine, but it may be also used as a meaning of particularly referring to wireless communication between an electronic device and an electronic device, namely, between machines. M2M terminals used in a cellular network may have lower performance or capability than that of typical terminals.
A lot of terminal may exist within a cell, and those terminals may be distinguished from one another based on its type, class, service, and the like.
For example, based on their operation type, terminals may be largely classified into a human type communication (HTC) terminal and a machine type communication (MTC) terminal. The machine type communication (MTC) may include communication between M2M terminals. Here, human type communication (HTC) may denote the transmission and reception of signals for which the transmission of signals is determined by a human, whereas MTC may denote the transmission of signals triggered by itself or event occurrence in each terminal or periodically without the intervention of a human.
Furthermore, if machine-to-machine (M2M) communication (or machine type communication (MTC)) is taken into consideration, then the number of whole terminals may suddenly increase. M2M terminal may have the following features based on support services.
1. A lot of terminal within a cell
2. Low amount of data
3. Transmission of low frequency (may have periodicity)
4. Limited number of data characteristics
5. Insensitive to time delay
6. Having low mobility or fixed
Furthermore, M2M communication may be used in various fields, such as protected access and surveillance, pursuit and discovery, public safety (emergency situation, disaster), payment (vending machine, ticket machine, parking meter), health care, remote control, smart meter, and the like.
Idle Mode
Idle mode is a mechanism capable of periodically receiving a downlink broadcast message without registering with a specific base station even when a terminal wanders in a wireless link environment having a plurality of base stations over a wide region.
Idle mode is a state in which only downlink synchronization is carried out to suspend all normal operations as well as handover (HO), and receive a paging message which is a broadcast message only for a predetermined interval. Paging message is a message for indicating paging action to a terminal. For example, the paging action may include ranging operation, network reentry, and the like.
Idle mode may be initiated by a terminal or initiated by a base station. In other words, the terminal may transmit a deregistration request (DREG-REQ) message to the base station, and receive a deregistration response (DREG-RSP) message in response to the deregistration request (DREG-REQ) message, thereby entering an idle mode. Furthermore, the base station may transmit a deregistration request (DREG-REQ) message or deregistration command (DREG-CMD) to the terminal, thereby entering an idle mode.
When a terminal receives a paging message corresponding to the terminal itself during an available interval (AI) in an idle mode, the terminal is switched to a connected mode through a network entry process with the base station to transmit and receive data.
Ranging
A user terminal performs a ranging process with the base station when accessing a network. The ranging process is a process for controlling a “time offset”, a “frequency offset”, and the like between the user terminal and base station and exchanging information such as management information. The user terminal may access the relevant network through such a ranging process, and performs a ranging process even when moving into a target base station through a handover procedure.
Furthermore, when the communication system is transited from an idle mode presented as a power reduction scheme of the user terminal to a normal operation mode, a network access should be attempted by selecting the best base station at a transition time point for the operation in the normal operation mode, and even at this time the ranging process is carried out. In this manner, the ranging process is carried out for various purposes.
The procedure of the ranging process may be typically classified into a code ranging and a RNG-REQ message ranging, and only the code ranging may be independently carried out, and the code ranging and RNG-REQ message ranging may be sequentially combined and carried out.
In describing the code ranging, it may be carried out using a process in which the user terminal transmits a specific CDMA code and the base station that has sensed the CDMA code responds using a RNG-RSP message. The base station determines whether or not it is required to control the “time offset”, “frequency offset”, and power of the relevant user terminal for a CDMA code index sensed by the base station itself, and the result is sent through a RNG-RSP message. The user terminal determines whether or not the code ranging attempted by the user terminal itself through receiving such a RNG-RSP message is successful, and then performs the required offset control.
The CDMA code is distinguished by a CDMA code index, and the user terminal should use a specific range of CDMA codes based on the purpose of the ranging operation. The base station grasps the purpose of the ranging process of the relevant user terminal based on a CDMA code index transmitted by the user terminal, and then performs a support corresponding to each purpose.
An uplink channel descriptor (UCD) message transmitted by the base station may include a parameter indicating a range of CDMA code indices supported by the relevant base station. The IEEE 802.16e standard may include the following information in the UCD message. The UCD message uses an uplink interval usage code (UIUC) used when the base station notifies the uplink region of each user terminal through UP-MAP. Each user terminal may know a modulation scheme/channel encoding scheme that should be applied to an uplink region assigned to the user terminal itself through the UIUC information. The UCD message may include information mapped with the UIUC value and modulation scheme/channel encoding scheme. Furthermore, the UCD information may include a range of CDMA codes that should be used for an operation such as “initial ranging”, “periodic ranging”, “bandwidth request”, “handover”, and the like.